The human spinal column is generally divided into three sections: the cervical, thoracic, and lumbar spine. Portions of the spine, known as vertebrae, are divided by intervertebral discs. Due to a variety of stresses and forces imparted upon the spinal column, damage to intervertebral discs is not uncommon. Conventional methods of treating and repairing damaged discs include spinal arthrodesis (i.e. spinal fusion) and surgical replacement of a disc with an artificial disc (i.e. disc arthroplasty).
When performing these and other procedures, it may be important or necessary to determine a specific location along the spinal column or among the various vertebral bodies, such as the center axis of the spinal column, so that the surgeon may locate and/or mark control parts for completing one of the various procedures conducted with reference thereto. Locating the center axis of a spine, however, may prove difficult given the variations in patient anatomy that may result from, for example, patient size, abnormalities of the spine and surrounding structure, and an absence of typical anatomical landmarks. Other problems that contribute to the difficulty of locating markers in a patient include limited visibility due to the presence of tissue, blood, etc., or the lack of adequate lighting, or the presence of tools or devices placed in the patient to complete the surgery. Locating markers within a patient during minimally invasive surgery may also be difficult due to visual constraints.
Methods for identifying working points about a spinal column utilizing radiographic means are known in the art. For example, U.S. Patent Application Publication No. 2007/0242869 to Luo et al., which is hereby incorporated by reference in its entirety, discloses a method for acquiring radiographic images of a spine and locating and calculating geometrical information, including the center line of the spine. However, images obtained by radiographic means may be of limited value in determining a center axis of the spine, may require additional expenditure of time, expense, and effort to obtain such images, sometimes resulting in misidentification or miscorrelation of anatomical features and radiographic images, etc. Moreover, obstructions resulting from a patient's size and the potential presence/absence of anatomic landmarks that are required to determine the center line by radiographic mapping create practical problems. The invention of Luo et al. and similar methods further subject the patient to radiation exposure which may be undesirable.
Various methods and devices which employ radiographic means suffer from various drawbacks and complications. These include, for example, the need to subject both a patient and a physician or user to radiation, time consuming preparation and administration of radiologic techniques, and the potential for inaccurate or inconclusive results due to the presence of anatomical anomalies or absence of anatomical landmarks.
Therefore, there is a need for an instrument and method capable of accurately and repeatedly identifying one or more points along a spinal column, such as a center axis of a spine. There is further need to economically and quickly, during a surgical procedure, determine these points or “markers” without relying upon radiographic imaging and that otherwise addresses the problems associated with prior art methods. The following disclosure describes an instrument that employs a novel combination of features that address these long felt needs and further describes a method for using the same.